1. Field of the Invention
The present invention relates to a flat liquid crystal display and in particular to a liquid crystal display reducing instantaneous current loaded by a scan driver during shutdown and power on processes of the liquid crystal display.
2. Description of the Related Art
FIG. 1 shows a schematic diagram of a conventional liquid crystal display. The liquid crystal display comprises a display array 10, a scan driver 11, a data driver 12, and a power device 13. The display array 10 is formed by interlacing data electrodes D11 to D1n and scan electrodes G11 to G1m. Each set of the interlacing data electrode and scan electrode corresponds to one display unit. The power device 13 applies a voltage signal V13 to the scan driver 11. In normal operation of the liquid crystal display, the scan driver 11 sequentially outputs the received voltage signal V13 to scan electrodes G11 to G1m according to a gate control signal. When receiving the scan signal, the scan electrode corresponding to a row turns on thin film transistors (hereinafter referred to as “TFT”) within all display units corresponding to the row. It is noted that signals carried on the scan electrodes G11 to G1m are generally called scan signals. Thus, in the following description of the related art, each signal output from the scan driver 11 to the scan electrodes G11 to G1m is referred to as a “scan signal” and a voltage level of each scan signal is at that of voltage signal V13.
When the TFTs within all display units corresponding to a row are all turned on, the data driver 12 outputs corresponding video signals with grayscale values to the n display units corresponding to the row through the data electrodes D11 to D1n according to image data prepared but not yet displayed. Each time the scan driver 11 finishes scanning all m rows, the operation to display a single frame is completed. Therefore, display images is achieved by repeatedly scanning the scan electrodes and outputting the video signals.
During shutdown and power on processes, an Xon function of the LCD detects large current and then generates an Xon signal. When detecting the signal Xon, the scan driver 11 outputs simultaneous scan signals to all the scan electrodes G11 to G1m to immediately turn on the TFTs within all the display units. As a result, discharge of each display unit is completed immediately, eliminating residual images and charges in the display units.
In normal operation, because the scan driver 11 sequentially outputs the scan signal to the scan electrodes G11 to G1m, output power of the power device 13 is dispersed. However, during shutdown and power on processes, the scan driver 11 detects the Xon signal and then simultaneously outputs the scan signals to all the scan electrodes G11 to G1m. The output power of the power device 13 is centralized. Thus, when the scan driver 11 simultaneously outputs the scan signals to all the scan electrodes G11 to G1m, a Vgh bonding area for transmitting the scan signals cannot load high power from the power device 13. After the liquid crystal display power on and off many times, holes occue in the Vgh bonding area, that is, high impedance occurs in the trace of the Vgh bonding area and impact the normal operation of the scan driver 11.